Why do I get the message 'download' for all my incoming texts?

[AC Question]

I have an HTC Desire 510 using Verizon Message+. I'm a total noob. Text messaging working fine for the first month of having the phone, now all of a sudden I can't get any text messages at all - each message box says 'download' and when I push it it says 'downloading.....' forever (seriously, I watched it for over 2 minutes) and then it goes back 'download' and there is nothing downloaded anywhere. I now have 20 messages that all just say 'download'. I have spoken with the people who sent the texts and they are simple text messages (no pictures, videos, nothing).